Paper and pulp mill sludges are generally the dewatered sludges that come from treatment of waste water from paper and pulp processes. That is, they are the suspended solids from paper making. A principal component of such materials is cellulose fiber, generally comprising around 40-80%, by weight, of the solids content and typically a large majority of the organics, contained within the solids. Much of the remainder of the solids weight of paper pulp mill sludges comprises various minerals and clays. Paper and pulp mill sludges generally result from operations for the production of papers, tissues and cardboard.
Paper mill sludge typically contains about 45% of the cellulose fiber from the paper processing. A de-inking sludge is the resulting pulp mill sludge from a waste paper recycling operation. It comprises up to 55% cellulose fiber and other materials from the process. Especially when the sludge results from recycled paper, such as a de-inking sludge, it may also contain a substantial amount of clay or other filler. If a paper or pulp bleaching operation has been involved, the sludge may also contain some chlorines or other contaminants.
Paper mill sludges and pulp sludges have, in the past, generally been waste materials with no commercial use or value. Generally disposition of large volumes of such sludges (as are generated yearly in the U.S.) has required commitment of large amounts of landfill area, equipment and personnel, to the handling of what has been little more than a waste byproduct. Also, environmental problems are created from the disposition of such materials. Indeed, in many locations such sludges are subjected to special disposition requirements such as storage in lined or capped landfills.
Fly ash (sometimes "coal combustion fly ash") is a waste product from coal burning operations, such as coal fired boiler operations for the generation of power. Herein the term "fly ash" is meant to refer to the "light" ash which is the particulate material collected from off gases of a coal burning operation, for example in an electrostatic precipitator or bag house. Such coal ash or fly ash generally comprises a mixture of silica and alumina, with lesser amounts of other minerals. It is generated in very large amounts in this country. The volumes in which it is produced have generally well exceeded any uses to which it has been placed. Thus, it is often disposed of through waste disposal operations such as landfilling. It can in some instances contain components which are hazardous, and thus sometimes special handling techniques are required for its disposition.
Sanitary waste ash (sometimes called "municipal waste ash", "water treatment waste ash" or "SAN") is the incinerated biological solids sifted out from a water treatment operation. Such material generally comprises the result of incinerating water treatment waste solids of about 70% or less solids content. It is a coarse material, somewhat like sand, usually having a dull orange color. It is, typically, predominantly alumina and silica. It is a waste product of water treatment operations, and has generally been a source of problems for disposition. In the past it has been of little value, and has generally been disposed of as landfill.